1. Field of the Invention
The present invention concerns a therapy system of the type having a therapy apparatus that produces therapeutic x-ray radiation.
2. Description of the Prior Art
The x-ray radiation in therapy systems involves energies in the range of approximately 4 to 20 MeV and is used, for example, for tumor radiation of patients. During operation, the radiation is directed to a treatment area of the system in which the patient is placed in the therapy system in such a way that the tumor is located in the treatment area.
By means of CT, MR or PET recordings, it is possible to determine precisely the position of the tumor in the patient. However, at the moment of therapeutic radiation, this position must be brought in alignment with the absolute coordinates or the room or the radiation device, i.e., the therapy system.
In this regard, it is known to produce an x-ray image of the patient once the patient has already been positioned or fixed in the therapy system. The x-ray image should be gene rated immediately prior to therapeutic x-ray radiation. In the case of highly movable tumors, for example, in the stomach or prostate gland of a patient, it is necessary to generate additional images in the continuous radiation cycle even during the period of radiation, in order to monitor the constantly changing location of the tumor and, if required, to reposition the patient.
It is also known to generate an x-ray image of the patient in an imaging system separate from the therapy system and to mark the position of the tumor by marking the skin of the patient. It is a disadvantage that, because of the possible movement of the tumor in relation to the skin of the patient, it is not possible to achieve a precise position in the therapy system.
There are also therapy systems that have additional x-ray tubes and detectors attached to the exterior of the system or its housing. In this way it is possible to obtain an image in parallel with the therapy. In this case, it is a disadvantage that these additional components make it difficult to attend to the patient.
The therapeutic x-ray radiation in the therapy system is produced by an electron accelerator, the energy of which usually can be controlled. It is also known to reduce the beam energy of the electron accelerator of the therapy system as far as possible and to perform so-called MV imaging (megavoltage imaging). Consequently, in order to produce an x-ray image the therapeutic x-ray beam is used which usually has energies in the MeV range. In this case, it is a disadvantage that energies below approximately 1 MeV are almost impossible with the specified electron accelerators. Therefore, x-ray radiation used for imaging is highly energetic, i.e., the image quality is not ideal and shows low contrast in displaying the soft tissue of the tumor tissue.
It is also known to immobilize the patient. This increases the reproducibility of the marked positions, for example on the skin of the patient, and also increases the possibility that the originally adjusted position of the patient is maintained during the treatment. However, this method cannot compensate any movement of the tumor in the patient and is therefore primarily used for tumors in the head region. In this case, it is a disadvantage that the patient usually feels uncomfortable.
In this regard, it is known to synchronize rapid or general movements of the tumor in the patient through gating, i.e., movement or location triggering of the therapeutic x-ray radiation. In this case, it is of disadvantage that such gating is inadequate with tumors in several organs, as, for example, in the intestines. This approach also results in an extension of the treatment time.